Exposure control is intended to address the fact that a photographic sensor has a physically limited useful exposure range often called its dynamic range. If, for any part of the photograph, the actual exposure is outside this range, the sensor will not capture the image accurately. For example bright scene areas which saturate the corresponding pixels (picture elements) of a sensor would be overexposed and will normally appear as bright spots, e.g., white areas in the case of black and white images.
In an attempt to ensure that an area of interest, e.g., subject, in a scene is captured accurately, automatic exposure control in digital cameras is sometimes based on user selection of a point of a displayed image to indicate a subject of interest. In such systems, the area around and including the selected point, e.g., a rectangular area, is then normally used as the basis for automated exposure control with all portions within the rectangular area being treated as being of equal importance for exposure control purposes. While this approach is satisfactory in many applications, it can have undesirable results where the subject occupies only a portion of the scene area around the selected point that is used for exposure control.
For example, consider the case where a thin portion, e.g., branch, of a tree is selected by a user of the camera as the subject of interest. A large portion of the area surrounding the branch selected as the subject of interest may correspond to the sky or some other distant object of little interest to the user. It should be appreciated that treating light corresponding to the sky or distant object for purposes of determining exposure control may result in an exposure which does not primarily reflect the light from the subject of interest, the tree branch, but rather the distant object. This can result in under and/or over exposure with respect to the actual identified subject of interest, e.g., the tree branch which emits much less light than the bright sky and is also at a very different distance from the camera than the sky or background adjacent the tree branch.
In view of the above discussion, it should be appreciated that there is a need for improved methods and/or apparatus for implementing exposure control. In view of the above discussion it should be appreciated that there is a need for exposure control methods which could take into consideration one or more factors other than simple proximity to a point identified as a subject of interest when making an exposure control determination.